This invention relates to a method of manufacturing polyesters with excellent heat resistance and adhesiveness to rubber and with reduced terminal carboxyl groups.
It is well known that reducing the terminal carboxyl groups (abbreviated "(COOH)" in the following) is effective in improving the heat resistance of polyesters, that is, their resistance to hydrolysis and amine decomposition at high temperatures. Various methods of reducing the (COOH) of polyesters have been proposed, but the most representative example of these methods is that of reacting polyesters and epoxy compounds (Japanese Public Patent Disclosure No. Showa 54 [1979] 6051). However, when the inventors investigated this method it was found that although the (COOH) of the polyester is reduced by adding the epoxy compound, there is also the problem that the degree of polymerization is lowered. On the other hand, concerning methods of improving adhesiveness between polyesters and rubber, various proposals have been made for modifying the rubber, etc., but it has been found that they have many problems, including their effectiveness, the complexity of their performance, etc.